This invention relates to solar stills, more particularly to the tilted tray type of solar still.
Solar operated stills for converting bore, brackish, impure or salt water into pure drinking water have been widely studied and reported since 1952 (Reference 1). The heat required for the operation of such a still can be provided by solar energy. However, it can also be used with any other source of input hot water, such as water heated by gas, electricity, wood or effluent etc.
In particular, stills of the absorbing panel type and variously described as; stepped tray, stacked tray or tilted tray are well known in principle to consist of an absorber panel having a plurality of interconnected calls containing a shallow layer or pond of impure water.
A glass panel positioned above the absorber panel and in close proximity to the water surface acts as a solar window, a condensing surface and a convection, minimising device.
The absorber panel and glass cover combination system is typically inclined to the horizontal at an angle of about 10xc2x0 thus preventing condensed droplet refluxing.
Commonly, the glass, outer surface is used for the collection of rainwater.
A description now follows of a patent application including various important and improved techniques and devices which are applicable to any such tilted tray system. Incorporation of these features singly or in combination into any existing system, will result in a considerable increase in the output of potable water as well as a greater convenience in operation with respect to optimised solar siting, solar energy collection, internal plumbing and cleaning of the absorber panel.
Thus there is provided in one form of the invention a solar still of the tilted tray type, said still including a glass cover and a plurality of individuals cells containing the solution to be evaporated, the solar still having means to cast a shadow to enable the solar still to be oriented with reference to the solar radiation to maximise the output of the solar still.
In a preferred form the means to cast the shadow includes a nodus to cast a shadow on a screen whereby the solar still can be orientated for any particular angle of incidence of the solar radiation.
In another form of the invention there is provided a solar absorber for heating a fluid, said absorber having a black panel to absorb th e solar radiation, the absorber including a reflector positioned beneath the panel to redirect the black-body radiation to be absorbed by the black panel to enhance the overall heat gain.
In a preferred form of the invention the solar absorber is a solar still of the sited tray type having a plurality of individual cells formed in a black panel, the reflector being a long wavelength reflector such as aluminium foil positioned directly beneath the base of the absorber panel.
Also in another form of the invention the solar still of the tilted tray type is provided with a drip check on the undersurface of the glass panel to ensure that the distilled product drips into an outlet channel.
In a further form of the invention the solar still has a plurality of individual cells formed in the black panel wherein some or all of the calls are provided with means to prevent or substantially eliminate distortion of the calls and the base due to heating of the base.
Preferably the panel is a plastic member, and the means to prevent or substantially eliminate distortion in the cells and base include a concave or convex portion in the panel or the cells.
In a still further form of the invention the solar still includes a black absorber panel having a plurality of individual cells, a glass sheet positioned above the cells in close proximity to the cells, preferably in the range of 10 to 20 mm above the uppermost portion of each cell.